Homeostatic regulation of potassium excretion

Multiple systems participate in the homeostatic regulation of potassium excretion. Changes in plasma potassium, above a baseline value, will directly stimulate potassium excretion. Acute variations in aldosterone may have only small and perhaps insignificant effects in stimulating potassium excretion when aldosterone is present within its normal plasma range, but may be highly significant in determining the kaliuretic response to changes in plasma potassium or tubular flow rate. Elevation of plasma aldosterone to supraphysiological levels appears to produce increases in potassium excretion. Chronic variations in aldosterone are important, but not unique in determining renal potassium adaptation to chronic variations in potassium uptake. New lines of evidence point to sensors of potassium intake located in the hepatic portal vein or liver, or in enteric locations. A reflex control of potassium excretion, first demonstrated by Aizman and Finkenshtein et al. [120-123] in the dog, and independently suggested in a more general form for the sheep, may be integral in the regulation of potassium excretion in response to intake. With this feedforward control system, potassium excretion may be regulated without changes in systemic plasma potassium concentration. From diverse lines of investigation we find that there is a compelling argument for an important role for the brain in regulating both potassium excretion and its ICF/ECF ratio. One may speculate, albeit on the basis of preliminary information, that separate but analogous systems exist for sodium and for potassium, each involving the brain and each acting through specific humoral factors. For sodium, evidence is accumulating for a ouabain-like humoral agent, perhaps originating in the brain, which modulates renal sodium excretion and the sodium concentration of ICF. Both of these actions have been proposed to have an important influence on blood pressure regulation. The evidence presented here is compatible with a similar system for potassium. On the basis of these studies reviewed here, it is intriguing to speculate that an analogous humoral factor is involved in the regulation of potassium homoeostasis, and that its effects, when understood, may help to resolve current debates regarding the role of potassium in blood pressure regulation.